Liquid ejection device and liquid ejection printer

ABSTRACT

A liquid ejection device includes: a drive waveform generator generating a drive waveform signal; a modulator performing pulse modulation on a signal from the drive waveform generator to provide a modulated signal; a digital power amplifier performing power amplification on the modulated signal to provide an amplified digital signal; a Lowpass Filter smoothing the amplified digital signal to provide a drive signal of an actuator; a compensator advancing the phase of the drive signal to provide a negative feedback signal; and a subtractor providing a differential signal between the drive waveform signal and the negative feedback signal as an input signal to the modulator.

BACKGROUND

1. Technical Field

The present invention relates to a liquid ejection device which performspower amplification on a drive signal to an actuator ejecting a liquid,and is suitable for a liquid ejection printer which prints characters,images, etc. by ejecting a minute liquid droplet out of a nozzle of aliquid ejection head and forming fine particles (dots) on a printingmedium.

2. Related Art

In a liquid ejection printer, an actuator such as a piezoelectricelement is provided and a predetermined drive signal has to be appliedto this actuator to eject a liquid out of a nozzle of a liquid ejectionhead. Since this drive signal has a relatively high voltage, it isnecessary to perform power amplification on a drive waveform signalserving as a reference of the drive signal by using a power amplifier.Therefore, in JP-A-11-204850, a digital power amplifier which has anextremely small power loss compared to an analog power amplifier and canbe made compact is used, pulse modulation is performed on a drivewaveform signal by a modulator to obtain a modulated signal, poweramplification is performed on the modulated signal by the digital poweramplifier to obtain an amplified digital signal, and the amplifieddigital signal is smoothed by a Lowpass Filter to obtain a drive signal.

However, when the actuator is a capacitive load such as a piezoelectricelement, the Lowpass Filter needs a damping resistor because of theabsence of a resistance component, resulting in a large power loss dueto this damping resistor. That is, as is well known, when a LowpassFilter is formed of a coil and a capacitor, there is a resonancefrequency represented by the inductance L of the coil and the capacity Cof the capacitor, and the presence of this resonance frequency makes itpossible to store power and attenuate voltage fluctuations correspondingto the modulation frequency. However, resonance sometimes occurs due tothe resonance frequency. When a resistance component is present in acircuit, the resonance is suppressed (attenuated) by the resistancecomponent; however, since a capacitive load such as a piezoelectricelement has no or an extremely small resistance component, the resonanceis not suppressed (attenuated) and remains. To suppress (attenuate) theremaining resonance, a circuit has to be provided with a resistor calleda damping resistor for suppressing (attenuating) the resonance, andpower is consumed when the damping resistor suppresses (attenuates) theresonance.

SUMMARY

An advantage of some aspects of the invention is to provide a liquidejection device and a liquid ejection printer that can reduce a powerloss due to a damping resistor.

A liquid ejection device according to an aspect of the inventionincludes a drive waveform generator generating a drive waveform signal,a modulator performing pulse modulation on a signal from the drivewaveform generator to provide a modulated signal, a digital poweramplifier performing power amplification on the modulated signal toprovide an amplified digital signal, a Lowpass Filter smoothing theamplified digital signal to provide a drive signal of an actuator, acompensator advancing the phase of the drive signal to provide anegative feedback signal, and a subtractor providing a differentialsignal between the drive waveform signal and the negative feedbacksignal as an input signal to the modulator.

According to this liquid ejection device, a resonance characteristicproduced when no damping resistor is used in the Lowpass Filter can becompensated for by a negative feedback signal. This eliminates the needfor a damping resistor, and makes it possible to reduce power loss. Thatis, since pulse modulation is performed on a differential signal betweenthe drive waveform signal and the negative feedback signal by themodulator, when, for example, resonance is produced in the drive signal,the differential signal corresponds to an inversion signal of theresonance produced in the drive signal. Thus, by performing pulsemodulation on the differential signal and performing power amplificationthereon and then adding the resultant signal to the drive signal, it ispossible to obtain the original drive signal.

The liquid ejection device may include an inverse filter providedbetween the drive waveform generator and the subtractor and correctingthe frequency characteristic of a closed loop formed of the modulator,the digital power amplifier, the Lowpass Filter, the capacitance of theactuator, and the compensator so as to be constant in a predeterminedfrequency domain.

According to this liquid ejection device, by correcting the frequencycharacteristic of a closed loop formed of the modulator, the digitalpower amplifier, the Lowpass Filter, the capacitance of the actuator,and the compensator, the frequency characteristic which changes with thenumber of actuators which are driven, so as to be constant in apredetermined frequency domain by the inverse filter, for example, it ispossible to ensure the accuracy of the drive signal.

A liquid ejection printer according to another aspect of the inventionuses the liquid ejection device described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic configuration front view showing a firstembodiment of a liquid ejection printer using a liquid ejection deviceof the invention.

FIG. 2 is a plan view of an area near a liquid ejection head used in theliquid ejection printer of FIG. 1.

FIG. 3 is a block diagram of a control device of the liquid ejectionprinter of FIG. 1.

FIG. 4 is an explanatory diagram of a drive signal driving an actuatorin each liquid ejection head.

FIG. 5 is a block diagram of a switching controller.

FIG. 6 is a block diagram showing an example of a drive circuit of theactuator.

FIG. 7 is a block diagram of a modulator of FIG. 6.

FIG. 8 is a block diagram of a digital power amplifier of FIG. 6.

FIG. 9 is a block diagram of a Lowpass Filter of FIG. 6.

FIG. 10 is a block diagram of a compensator of FIG. 6.

FIG. 11 is an explanatory diagram of the frequency characteristic of theLowpass Filter of FIG. 9.

FIG. 12 is an explanatory diagram of a closed loop formed of amodulator, a digital power amplifier, a Lowpass Filter, an actuator, anda compensator.

FIG. 13 is an explanatory diagram of a correction of the frequencycharacteristic of the closed loop, the correction made by thecompensator.

FIG. 14 is a block diagram of an actuator drive circuit showing a secondembodiment of the liquid ejection printer using the liquid ejectiondevice of the invention.

FIG. 15 is an explanatory diagram of a closed loop in the actuator drivecircuit of FIG. 14.

FIG. 16 is an explanatory diagram of a correction of the frequencycharacteristic of the closed loop, the correction made by an inversefilter.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As a first embodiment of a liquid ejection device of the invention, aliquid ejection device used in a liquid ejection printer will bedescribed.

FIG. 1 is a schematic configuration diagram of a liquid ejection printerof the first embodiment. This liquid ejection printer is a line headprinter in which a printing medium 1 is conveyed from left to right inan arrow direction in FIG. 1 and printing is performed thereon in aprinting region located along a path on which the printing medium 1 isbeing conveyed.

In FIG. 1, a plurality of liquid ejection heads 2 are provided above aconveying line of the printing medium 1. The liquid ejection heads 2 aredisposed so that they form two lines in a printing medium conveyingdirection and are arranged next to one another in a directionintersecting the printing medium conveying direction, and are fixed to ahead fixing plate 11. On the lowermost face of each liquid ejection head2, a large number of nozzles are formed, and this face is called anozzle face. As shown in FIG. 2, the nozzles are disposed, according toa color of a liquid to be ejected, in a line in a direction intersectingthe printing medium conveying direction. The line is called a nozzleline, and the line direction is called a nozzle line direction. Thenozzle lines of all the liquid ejection heads 2 disposed in a directionintersecting the printing medium conveying direction form a line headrunning along the width in a direction intersecting the direction inwhich the printing medium 1 is conveyed. When the printing medium 1passes under the nozzle faces of these liquid ejection heads 2, a liquidis ejected from a large number of nozzles formed on the nozzle faces,and printing is performed.

To the liquid ejection heads 2, ink liquids of four colors: yellow (Y),magenta (M), cyan (C), and black (K), for example, are supplied fromunillustrated liquid tanks through liquid supplying tubes. The requiredamount of liquid is ejected at a proper area simultaneously out of thenozzles formed in the liquid ejection heads 2, whereby fine dots areformed on the printing medium 1. A liquid of each color is ejected,whereby printing can be performed by passing the printing medium 1 underthe nozzle faces once, the printing medium 1 being conveyed by aconveying section 4.

Methods for ejecting the liquid out of the nozzles of the liquidejection heads 2 include an electrostatic system, a piezo system, a filmboiling liquid ejection system, etc.; in this embodiment, the piezosystem is used. The piezo system is a system in which, when a drivesignal is fed to a piezoelectric element which is an actuator, avibrating plate in a cavity is displaced, causing a pressure changeinside the cavity, and the liquid is ejected out of the nozzle due tothe pressure change. By adjusting a peak value or a voltage increase anddecrease gradient of the drive signal, it is possible to adjust theejection amount of the liquid. The invention can also be appliedsimilarly to a liquid ejection method other than the piezo system.

The conveying section 4 for conveying the printing medium 1 in aconveying direction is provided under the liquid ejection heads 2. Theconveying section 4 is formed by winding a conveying belt 6 around adriving roller 8 and a driven roller 9, and an unillustrated electricmotor is connected to the driving roller 8. Inside the conveying belt 6,an unillustrated sticking apparatus for making the printing medium 1stuck to the surface of the conveying belt 6 is provided. As thesticking apparatus, for example, an air sucking apparatus which makesthe printing medium 1 stuck to the conveying belt 6 by negative pressureor an electrostatic sticking apparatus which makes the printing medium 1stuck to the conveying belt 6 by electrostatic force is used. Therefore,when only one sheet of printing medium 1 is fed on the conveying belt 6by a paper feed roller 5 from a paper feed section 3 and the drivingroller 8 is driven and rotated by the electric motor, the conveying belt6 is rotated in the printing medium conveying direction, and theprinting medium 1 is conveyed while being stuck to the conveying belt 6by the sticking apparatus. Printing is performed by ejecting the liquidfrom the liquid ejection heads 2 while the printing medium 1 is beingconveyed. The printing medium 1 on which printing has been performed isejected into a paper ejection section 10 located downstream in theconveying direction. A printing reference signal output apparatus formedof a linear encoder, for example, is attached to the conveying belt 6.Exploiting the fact that the conveying belt 6 and the printing medium 1which is conveyed while being stuck to the conveying belt 6 are moved insynchronization with each other, the printing reference signal outputapparatus outputs a pulse signal corresponding to a printing resolutionwhich is required with the movement of the conveying belt 6 after theprinting medium 1 has passed a predetermined position on a conveyingpath, and outputs a drive signal according to the pulse signal from adrive circuit, which will be described later, to an actuator 22, therebyejecting a liquid of a predetermined color at a predetermined positionon the printing medium 1 and forming a predetermined image on theprinting medium 1 by the dots of the liquid.

In the liquid ejection printer using the liquid ejection device of thisembodiment, a control device for controlling the liquid ejection printeris provided. As shown in FIG. 3, this control device includes an inputinterface 61 for reading the printing data input from a host computer60, a control unit 62 which is formed of a microcomputer performingcomputing such as print processing based on the printing data input fromthe input interface 61, a paper feed roller motor driver 63 controllingthe driving of a paper feed roller motor 17 connected to the paper feedroller 5, a head driver 65 controlling the driving of the liquidejection head 2, an electric motor driver 66 controlling the driving ofan electric motor 7 connected to the driving roller 8, and an interface67 connecting the paper feed roller motor driver 63, the head driver 65,and the electric motor driver 66 with the paper feed roller motor 17,the liquid ejection head 2, and the electric motor 7.

The control unit 62 includes a CPU (central processing unit) 62 aperforming various types of processing such as print processing, RAM(random access memory) 62 c which temporarily stores printing data inputvia the input interface 61 or various data used when, for example, printprocessing is performed by using the printing data, or temporarilyexpands a program product for print processing etc., and ROM (read-onlymemory) 62 d formed of nonvolatile semiconductor memory storing acontrol program product etc. executed by the CPU 62 a. When the controlunit 62 obtains printing data (image data) from the host computer 60 viathe input interface 61, the CPU 62 a executes predetermined processingon this printing data, calculates nozzle selection data (drive pulseselection data) on a nozzle out of which the liquid is ejected or theamount of liquid to be ejected, and outputs a drive signal and a controlsignal to the paper feed roller motor driver 63, the head driver 65, andthe electric motor driver 66 based on the printing data, the drive pulseselection data, and the input data from various sensors. The paper feedroller motor 17, the electric motor 7, the actuator 22 in the liquidejection head 2, and the like, are individually activated by the drivesignal and the control signal, whereby the printing medium 1 is fed,conveyed, and ejected and print processing is performed on the printingmedium 1. The component elements in the control unit 62 are electricallyconnected via an unillustrated bus.

In FIG. 4, an example of a drive signal COM which is fed to the liquidejection head 2 from the control device of the liquid ejection printerusing the liquid ejection device of this embodiment and drives theactuator 22 formed of a piezoelectric element is shown. In thisembodiment, the drive signal COM is assumed to be a signal having avoltage changing with an intermediate voltage at the center. The drivesignal COM is a signal obtained as drive pulses PCOM connected inchronological order, the drive pulses PCOM which are unit drive signalsfor driving the actuator 22 to eject the liquid. A rising edge of thedrive pulse PCOM corresponds to a stage at which the liquid is drawn(for a face to which the liquid is ejected, it can be said that themeniscus is drawn) by increasing the volume of the cavity (the pressurechamber) communicating with the nozzle. A trailing edge of the drivepulse PCOM corresponds to a stage at which the liquid is pushed out (fora face to which the liquid is ejected, it can be said that the meniscusis pushed out) by reducing the volume of the cavity, and the liquid isejected out of the nozzle as a result of the liquid being pushed out.

By variously changing a voltage increase and decrease gradient or a peakvalue of the drive pulse PCOM formed of a voltage trapezoidal wave, itis possible to change the amount of drawn liquid, the rate at which theliquid is drawn, the amount of liquid pushed out, and the rate at whichthe liquid is pushed out. This makes it possible to change the amount ofliquid to be ejected and obtain dots of different sizes. Therefore, evenwhen a plurality of drive pulses PCOM are connected in chronologicalorder, the liquid is ejected by selecting a single drive pulse PCOM fromamong the drive pulses PCOM and feeding the drive pulse PCOM to theactuator 22 or the liquid is ejected multiple times by selecting aplurality of drive pulses PCOM from among the drive pulses PCOM andfeeding the drive pulses PCOM to the actuator 22, whereby it is possibleto obtain dots of various sizes. That is, putting the liquid in the sameposition multiple times before the liquid is dried out is substantiallyidentical to ejecting a large droplet of liquid. Thus, it is possible toincrease the size of a dot. By combining the techniques in this way, itis possible to realize multistep gradation. A drive pulse PCOM 1 on thefar left in FIG. 4 only draws the liquid and does not pushes out theliquid. This is called micro-vibration, and is used for suppressing andpreventing the thickening of the nozzle without ejecting the liquid.

To the liquid ejection head 2, in addition to the drive signal COM,drive pulse selection data SI&SP selecting a nozzle out of which theliquid is ejected based on the printing data and determining connectingtiming with which the actuator 22 such as a piezoelectric element isconnected to the drive signal COM, a latch signal LAT and a channelsignal CH which connect the drive signal COM and the actuator 22 of theliquid ejection head 2 based on the drive pulse selection data SI&SPafter the nozzle selection data is input to all the nozzles, and a clocksignal SCK for transmitting the drive pulse selection data SI&SP to theliquid ejection head 2 as a serial signal are input as a control signalfrom the control device of FIG. 3. Hereinafter, a minimum unit of thedrive signal driving the actuator 22 is referred to as a drive pulsePCOM, and the whole signal obtained as the drive pulses PCOM connectedin chronological order is referred to as a drive signal COM. That is,with the latch signal LAT, a series of drive signals COM is started tobe output, and the drive pulse PCOM is output with each channel signalCH. Of the drive pulse selection data SI&SP, the drive pulse selectionidentification data SI is 2-bit data indicating which drive pulse PCOMis selected from among the above-described drive pulses PCOM, and SP is16-bit selection switch control data for performing on/off control of aselection switch, which will be described later, in accordance with thetiming of the selected drive pulse PCOM.

In FIG. 5, a specific configuration of a switching controller configuredin the liquid ejection head 2 for feeding the drive signal COM (thedrive pulse PCOM) to the actuator 22 is shown. The switching controllerincludes a register 211 storing the drive pulse selection data SI&SP forspecifying the actuator 22 such as a piezoelectric element correspondingto the nozzle out of which the liquid is ejected, a latch circuit 212temporarily storing the data of the register 211, and a level shifter213 connecting the drive signal COM (the drive pulse PCOM) to theactuator 22 such as a piezoelectric element by performing levelconversion of the output of the latch circuit 212 and feeding the outputto the selection switch 201.

To the register 211, the drive pulse selection data SI&SP is inputaccording to the input pulse of the clock signal SCK, and the selectionswitch control data SP is stored in a predetermined address. The latchcircuit 212 latches the output signals of the register 211 by the inputlatch signal LAT after the selection switch control data SP of all theactuators is stored in the register 211. The signal stored in the latchcircuit 212 is converted by the level shifter 213 into a voltage levelwhich can turn on/off the selection switch 201 in the following stage.This is because the drive signal COM (the drive pulse PCOM) is a voltagehigher than the output voltage of the latch circuit 212 and theoperating voltage range of the selection switch 201 is set at a highlevel accordingly. Therefore, the actuator 22 such as a piezoelectricelement with the selection switch 201 which is closed by the levelshifter 213 is connected to the drive signal COM (the drive pulse PCOM)with the connection timing of the drive pulse selection data SI&SP (theselection switch control data SP). After the drive pulse selection dataSI&SP (the selection switch control data SP) of the register 211 isstored in the latch circuit 212, the next printing information is inputto the register 211, and the stored data of the latch circuit 212 issequentially updated according to the timing with which the liquid isejected. A sign HGND in the drawing denotes a ground end of the actuator22 such as a piezoelectric element. Thanks to the selection switch 201,even after the actuator 22 such as a piezoelectric element isdisconnected from the drive signal COM (the drive pulse PCOM), the inputvoltage of the actuator 22 is maintained at a voltage just before thedisconnection.

In FIG. 6, a schematic configuration of a drive circuit of the actuator22 is shown. This actuator drive circuit is configured in the controlunit 62 and the head driver 65 which are provided in the controlcircuit. The drive circuit of this embodiment includes a drive waveformgenerator 25 generating a drive waveform signal WCOM from which a drivesignal COM (a drive pulse PCOM) is generated, that is, the drivewaveform signal WCOM which serves as a reference of a signal controllingthe driving of the actuator 22, an adder-subtractor 31 serving as asubtractor outputting a difference between the drive waveform signalWCOM generated by the drive waveform generator 25 and a negativefeedback signal from a compensator, which will be described later,specifically, a differential signal WCOMdef obtained by subtracting anegative feedback signal from the drive waveform signal WCOM, amodulator 26 outputting a modulated signal PWM by performing pulsemodulation on the differential signal WCOMdef from the adder-subtractor31, a digital power amplifier 28 performing power amplification on themodulated signal PWM from the modulator 26 and outputting an amplifieddigital signal APWM, a Lowpass Filter 29 smoothing the amplified digitalsignal APWM from the digital power amplifier 28 and outputting theresultant signal as a drive signal COM, and a compensator 32 advancingthe phase of the drive signal COM and outputting a negative feedbacksignal CPST.

The drive waveform generator 25 holds and outputs the drive waveformdata DWCOM read from the waveform memory for a predetermined samplingperiod.

As the modulator 26 performing pulse modulation on the drive waveformsignal WCOM, as shown in FIG. 7, a well-known pulse width modulation(PWM) circuit is used. The pulse width modulation circuit includes atriangular wave oscillator 34 outputting a triangular wave signal havinga predetermined frequency and a comparison section 35 comparing thetriangular wave signal with the drive waveform signal WCOM andoutputting a modulated signal PWM with pulse duty cycle in which on dutycycle comes when the drive waveform signal WCOM is greater than thetriangular wave signal, for example.

The drive waveform generator 25, the adder-subtractor 31 which is asubtractor, and the modulator 26 can also be configured by computingperformed by a program product. As the modulator 26, a well-known pulsemodulation circuit such as a pulse density modulation (PDM) circuit canbe used instead.

As shown in FIG. 8, the digital power amplifier 28 includes ahalf-bridge output stage 21 formed of a high-side switching element Q1and a low-side switching element Q2 for substantially amplifying powerand a gate drive circuit 30 for adjusting gate-source signals GH and GLof the high-side switching element Q1 and the low-side switching elementQ2 based on the modulated signal PWM from the modulator 26. In thedigital power amplifier 28, when the modulated signal is at high level,the gate-source signal GH of the high-side switching element Q1 becomeshigh level, and the gate-source signal GL of the low-side switchingelement Q2 becomes low level. Therefore, the high-side switching elementQ1 is brought into an on state, and the low-side switching element Q2 isbrought into an off state. As a result, the output voltage Va of thehalf-bridge output stage 21 becomes a supply voltage VDD. On the otherhand, when the modulated signal is at low level, the gate-source signalGH of the high-side switching element Q1 becomes low level, and thegate-source signal GL of the low-side switching element Q2 becomes highlevel. Therefore, the high-side switching element Q1 is brought into anoff state, and the low-side switching element Q2 is brought into an onstate. As a result, the output voltage Va of the half-bridge outputstage 21 becomes 0.

When the high-side switching element Q1 and the low-side switchingelement Q2 are digitally driven in this way, a current flows through theswitching element in an on state, but the drain-source resistance valueis extremely small and therefore losses hardly occur. Since no currentflows through the switching element in an off state, no losses occur.Therefore, the loss itself of the digital power amplifier 28 isextremely small, and a switching element such as a small MOS FET can beused.

As shown in FIG. 9, as the Lowpass Filter 29, a secondary low-passfilter formed of one capacitor C and one coil L is used. A modulationfrequency generated in the modulator 26, that is, a frequency componentof pulse modulation is attenuated and removed by using this LowpassFilter 29, and a drive signal COM is output to the actuator 22 via theselection switch 201.

As shown in FIG. 10, the compensator 32 is formed of a high-pass filterwhich is formed of one capacitor C1 and one resistor R and outputs anegative feedback signal CPST by advancing the phase of a drive signalCOM. By making the resistor R of the compensator 32 have a largeresistance value, it is possible to reduce the value of a currentflowing through the resistor R and reduce power loss.

As shown by the solid line in FIG. 11, the frequency characteristic ofthe Lowpass Filter 29 of the first embodiment, the Lowpass Filter 29with no damping resistor, shows resonance near an attenuation startfrequency of the low-pass filter. Such gain fluctuations are notdesirable, and a frequency characteristic shown by the chaindouble-dashed line in FIG. 11, the frequency characteristic in which again is constant until an attenuation start frequency, is ideal. In thefield of audio, an ideal frequency characteristic can be sometimesobtained without adding a damping resistor due to the influence of afloating resistor or the like. However, since the actuator of the firstembodiment, the actuator 22 formed of a capacitive load such as apiezoelectric element, has no resistance component, a damping resistoris indispensable to achieve the frequency characteristic shown by thechain double-dashed line with the Lowpass Filter 29 itself, and thisdamping resistor results in an increase in power loss.

In the actuator drive circuit of the first embodiment, a closed loopformed of the adder-subtractor 31, the modulator 26, the digital poweramplifier 28, the Lowpass Filter 29 (actually, the capacitance of theactuator 22 formed of a capacitive load such as a piezoelectric elementis connected in parallel with the capacitor C in the Lowpass Filter 29),and the compensator 32 is depicted as shown in FIG. 12. Let the gain andthe transfer characteristic of a drive signal output system formed ofthe modulator 26, the digital power amplifier 28, and the Lowpass Filter29 (including the capacitance of the actuator 22 which is driven) be Aand H, respectively. Then, the above-mentioned frequency characteristicwith resonance is expressed as AH as shown in FIG. 13. On the otherhand, let the transfer characteristic of the compensator 32 be β. Then,the transfer characteristic G of the closed loop shown in FIG. 12 isexpressed in the following formula (1).

$\begin{matrix}{{G( f_{0} )} = {\frac{A \cdot {H( f_{0} )}}{1 + {A \cdot {H( f_{0} )} \cdot {\beta( f_{0} )}}} = \frac{1}{{\beta( f_{0} )} + \frac{1}{A \cdot {H( f_{0} )}}}}} & (1)\end{matrix}$

Therefore, it is necessary simply to set the transfer characteristic βof the compensator 32 so that the transfer characteristic G of theclosed loop is constant until a predetermined attenuation startfrequency as shown by the chain double-dashed line in FIG. 13.Specifically, since, for example, 1/(A·H) in formula (1) is shown by thebroken line in the drawing, when β+1/(A·H) becomes like the alternatelong and short line in the drawing by setting the transfercharacteristic β of the compensator 32 as shown by the solid line, thetransfer characteristic G of the closed loop can be set as shown by thechain double-dashed line. As mentioned above, power loss occurs due tothe current flowing through the resistor R of the compensator 32.However, it is possible to reduce the current value by increasing theresistance value of the resistor R and reduce the power loss.

As described above, in the liquid ejection device of the firstembodiment, when a drive waveform signal WCOM is generated by the drivewaveform generator 25, pulse modulation is performed on the signal fromthe drive waveform generator 25 by the modulator 26, power amplificationis performed on the modulated signal PWM by the digital power amplifier28, and the amplified digital signal APWM is smoothed by the LowpassFilter 29 to obtain a drive signal COM (a drive pulse PCOM) of theactuator 22, the phase of the drive signal COM (the drive pulse PCOM) isadvanced by the compensator 32 to obtain a negative feedback signalCPST, and the adder-subtractor 31 which is a subtractor inputs adifferential signal WCOMdef between the drive waveform signal WCOM andthe negative feedback signal CPST to the modulator 26 as an inputsignal. As a result, it is possible to compensate for the resonancecharacteristic produced when no damping resistor is used in the LowpassFilter 29 by using the negative feedback signal CPST. This eliminatesthe need for a damping resistor and reduce power loss.

Next, a second embodiment of the liquid ejection device of the inventionwill be described. As in the case with the first embodiment describedabove, the liquid ejection device of this embodiment is a liquidejection device applied to a liquid ejection printer, and a schematicconfiguration, an area near a liquid ejection head, a control device, adrive signal, and a switching controller are the same as those in thefirst embodiment. Therefore, in the following description, suchcomponents as are similar to those in the first embodiment areidentified with the same reference numerals and signs, and theexplanations thereof will be omitted. In the second embodiment, aninverse filter 23 is provided between the drive waveform generator 25and the adder-subtractor 31. The inverse filter 23 includes a controlunit, and can control its own frequency characteristic according to thenumber of actuators 22 which are driven. As is well known, the inversefilter 23 can be configured by computing performed by a program product.Therefore, the inverse filter 23 including the control unit can also beconfigured in the control unit 62 in the control circuit describedabove. That is, all the component elements from the drive waveformgenerator 25 to the modulator 26 can be digitized.

In the actuator drive circuit in the second embodiment, a closed loopformed of the adder-subtractor 31, the modulator 26, the digital poweramplifier 28, the Lowpass Filter 29, the capacitance of the actuator 22,and the compensator 32 is shown in FIG. 15. The transfer characteristicof the inverse filter 23 is assumed to be C. The transfer characteristicGO of the whole system including the inverse filter 23 is expressed inthe following formula (2).

$\begin{matrix}\begin{matrix}{{{C( f_{0} )} \cdot {G( {f_{0},N} )}} = {{C( f_{0} )}\frac{A \cdot {H( {f_{0},N} )}}{1 + {A \cdot {H( {f_{0},N} )} \cdot {\beta( f_{0} )}}}}} \\{= {G\; 0}}\end{matrix} & (2)\end{matrix}$

As described in WO 2007/083669, for example, when the number ofactuators 22 which are driven changes, the frequency characteristic ofthe closed loop changes. The feature is shown in FIG. 16. In this case,as mentioned above, since the resonance of the closed loop is suppressedby the negative feedback signal CPST from the compensator 32, thefrequency characteristic changes as the attenuation start frequencychanges, and the larger the number of actuators 22 which are driven is(the heavier the load is), the lower the attenuation start frequencybecomes.

Therefore, as the characteristic of the inverse filter 23, as shown bythe broken line in FIG. 16, it is necessary simply to increase theattenuation start frequency when the number of actuators 22 is large(the load is heavy) by using a so-called high-pass filter by which ahigh frequency band is emphasized. The number of actuators 22 which aredriven can be determined based on the drive pulse selection data SI&SP.Thus, when the inverse filter 23 is a high-pass filter, for example, bycontrolling the gain of the high-pass filter according to the number ofactuators 22 which are driven, it is possible to make the gain of theclosed loop constant in a predetermined frequency domain. As a result,an attenuation start frequency required for the Lowpass Filter 29 can bemaintained constant.

As described above, in the liquid ejection device of the secondembodiment, by correcting the frequency characteristic of the closedloop formed of the modulator 26, the digital power amplifier 28, theLowpass Filter 29, the capacitance of the actuator 22, and thecompensator 32, the frequency characteristic which changes with thenumber of actuators 22 which are driven, so as to be constant in apredetermined frequency domain by the inverse filter 23, it is possibleto ensure the accuracy of the drive signal.

In the embodiments described above, only a case in which the liquidejection device of the invention is applied to a line head liquidejection printer has been described in detail; however, the liquidejection device of the invention can also be applied similarly to amultipath liquid ejection printer.

The liquid ejection device of the invention can also be embodied as aliquid ejection device that ejects any liquid (including not only aliquid, but also a liquid substance in which particles of functionalmaterial are dispersed and a fluid substance such as gel) other than inkand a fluid other than a liquid (such as a solid that can be ejected asa fluid). For example, the liquid ejection device of the invention maybe a liquid ejection device that ejects a liquid substance containingdispersed or dissolved material such as electrode material or colormaterial which is used in the production of a liquid crystal display, anEL (electroluminescence) display, a surface emitting display, and acolor filter, a liquid ejection device that ejects a bioorganicsubstance used in the production of a biochip, and a liquid ejectiondevice that is used as a precision pipette and ejects a liquid used as asample. Furthermore, the liquid ejection device of the invention may bea liquid ejection device that ejects lubricating oil to a precisioninstrument such as a clock and a camera at a proper point with a highdegree of accuracy, a liquid ejection device that ejects, to asubstrate, a transparent resin liquid such as ultraviolet curable resinfor forming a micro hemispherical lens (an optical lens) or the likeused in an optical communication element etc., a liquid ejection devicethat ejects an etching liquid such as an acid or alkali for etching asubstrate etc., a fluid substance ejection device that ejects gel, and afluid ejection recording apparatus that ejects a solid such as powderlike toner. Moreover, the liquid ejection device of the invention may bea liquid ejection device used as a surgical instrument that incises orexcises a living tissue by ejecting a liquid such as water or a saltsolution in pulses. The invention can be applied to any one of theseejection devices.

This application claims priority to Japanese Patent Application No.2009-257375, filed on Nov. 10, 2009, the entirety of which is herebyincorporated by reference.

1. A liquid ejection device comprising: a drive waveform generatorgenerating a drive waveform signal; a modulator performing pulsemodulation on a signal from the drive waveform generator to provide amodulated signal; a digital power amplifier performing poweramplification on the modulated signal to provide an amplified digitalsignal; a lowpass filter smoothing the amplified digital signal toprovide a drive signal of an actuator; a compensator advancing a phaseof the drive signal to provide a negative feedback signal; and asubtractor providing a differential signal between the drive waveformsignal and the negative feedback signal as an input signal to beinputted to the modulator.
 2. The liquid ejection device according toclaim 1, further comprising: an inverse filter provided between thedrive waveform generator and the subtractor and correcting the frequencycharacteristic of a closed loop formed of the modulator, the digitalpower amplifier, the lowpass filter, the capacitance of the actuator,and the compensator so as to be constant in a predetermined frequencydomain.
 3. A liquid ejection printer comprising the liquid ejectiondevice according to claim 1.